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Design Issues with Wearables From the Perspective of Electromechanical Components

Life Alert's “I've fallen and I can't get up®!” became one of the most famous infomercial catchphrases in the late 1980s. The company's device, targeted at senior citizens, provided users at the time with the simple, yet revolutionary ability to call for emergency assistance at the push of a button. As you may have guessed, this was one of the first mass-produced medical wearables available on the market.

Wearables, also referred to more cumbersomely as wearable computers, encompasses all devices that can be worn on the body. This definition covers everything from pacemakers and activity trackers such as fitness wristbands and watches, through to smartwatches. More and more people suffering from chronic conditions are using these digital aides to improve their quality of life and manage their health issues; however, wearables have evolved over time and are no longer only lifesaving devices, but also real fashion accessories too, with current items on the market including activity-tracking wristbands, smartwatches, smart glasses, and even GPS-enabled shoes. In other words, wearables have been around for a long time, but are only now on the cusp of making a truly major breakthrough thanks to the developments currently being seen on the sensor and wireless markets.

The extent to which wearables are about to take the market by storm is clear when you consider that in the third quarter of 2017 alone, wearables saw growth of 7.3% compared to the previous year with 26.3 million units sold, according to a report by the IDC's Worldwide Quarterly Wearable Device Tracker 2017. This shows that it has been a long time since these devices were used for simple applications such as displaying pulse rates for joggers, but that they can now be used by people to get a general overview of their own fitness levels. Consumers are becoming increasingly interested in smart wearables (devices that execute third-party-provider applications), and less so in wearable computer systems that are only capable of fulfilling straightforward functions. This shift towards multifunctional devices is presenting the biggest names in wearables with the challenge of striking the right balance between practicality and design. Electromechanical input components are also firmly in focus.

According to Eric Ewing, Senior Product Manager at Panasonic, “From an electromechanical perspective, a wristwatch and a smartwatch are polar opposites, and each requires a different design. The crown of an analog wristwatch is very seldom used, as it is only there to set the time and manually wind the battery (power reserve). On a smartwatch, the electromechanical input component is used to switch between various different display fields, scroll through the menu, and individually configure settings — push notifications can be managed, weekly fitness performance levels can be calculated, and music tracks can be selected, etc.

“As such, contact and operability are of paramount importance, as these are what initially create the smartwatch experience — a satisfying, tactile experience or a positive ‘click feeling’ needs to be generated, a high life-cycle must be guaranteed, and consistency of operation needs to be ensured.” In other words, the more functions and possibilities that are designed and incorporated into the terminal device, the more important the choice of switch becomes.

IP67 tactile switch enclosure

The Right Force/Travel Ratio

The feel plays an important role when it comes to controls, as already mentioned, and can be designed specifically in line with customers’ preferences. In terms of the tactile experience — for example, for tactile switches — attention primarily needs to be paid to the actuation force to be applied to the switch.

Every tactile switch has its own unique set of characteristics that are expressed, for example, in the click ratio (see Figure 1). The click ratio describes the tangible resistance offered by a switch when it is used. The higher the click ratio, the crisper and snappier the switch feels. High-quality switches usually guarantee a service life of 100,000 to 1,000,000 switching cycles, depending on the push force. Like the force/travel ratio, the average service life (switching cycles) for each switch is also specified in its data sheet.

Figure 1. The click ratio describes the tangible resistance offered by a switch when it is used.

Most portable consumer electronic devices and wearables require relatively high click ratios and shorter travel distances (short stroke). This ensures that the operation creates feedback for the user and a sense of quality. You might understandably ask at this point, “Aren't all wearables the same?” No — there are exceptions, as the part of the body where the wearables are ultimately used also plays just as important a role.

“Weight is the most important factor for wearables that are worn on the head such as listening devices and smart glasses,” said Ewing. “A light actuation force is what is called for here, as these devices are outside of the user's direct field of vision and must be able to be operated with a delicate touch. The use of switches with a light actuation force (push force) also rules out any risk of injury.

“The situation with regard to wearables that are easily accessible and within the user's direct field of vision is different. Here, the electromechanical components are set up to reflect a high actuation force (high operation force). Specifically, in the case of smartwatches, the switches are usually activated via the user's pinch grip strength or even thumb pressure, whereby the thumb is pressed against the lower edge of the device while the index finger operates the switch. The potential strength of this force that is applied to the switch is best exemplified by the fact that rock climbers can pull themselves up with just their pinch grip strength. The advantage of such an electromechanical design is that the switch constitutes direct feedback for users and can withstand operating errors such as accidental knocks and bumps better, which is a compelling design feature for wearables in the sports market.”

Tactile switches for wearables also need to be able to work properly in harsh environments over many years. As such, protection against undesirable water, damp, moisture, and dust penetration, etc. must also be insured. This has less to do with the water tightness of the device (the construction of the product plays a much bigger role here) and more to do with the fact that the switches also have to be usable for a long time under the same conditions, and shouldn't present any signs of early wear as a result. Such requirements are specified, for example, by the IP67 protection rating for the housings of switches. An adhesively bonded silicone membrane is commonly used for this purpose; however, silicone ages relatively quickly and also loses its elasticity over time.

In manufacturing IP67 tactile switches, Panasonic uses a patented laser welding process (see Figure 2) in which the switch is sealed with a thin nylon film that is applied over the switch actuator. This safeguards the feel of the switch and protects it from developing any signs of wear. An IP67-certified version is particularly advisable for fitness-related wearables. Since users keep the devices in their hands, on their feet, or on their heads, they are exposed to the body parts that produce the most sweat.

Figure 2. In the laser welding process, the switch is sealed with a thin nylon film that is applied over the switch actuator.

“It's not really water, but the salt in the sweat that presents the greatest threat to the maintenance-free usage of switches,” said Ewing. “If you wear a Bluetooth headset when working out, the following issue occurs: the sweat drips down the cable directly into the mechanism that operates the volume control and the microphone. If it is not waterproof in accordance with the IP67 rating, then sweat will get into the switch. After you have finished using the device, what remains is the salt from the sweat, which can jam and destroy the switch.”

Will Touchscreens be the Death of Switches?

Touchscreens are seen as one of the most interactive and intuitive interfaces between man and machine, and rightly so, which could explain the success of smartphones and tablets. When it comes to choosing a user interface for wearables, though, the right choice must be determined based on functionality and energy consumption.

Touchscreens are only suitable for wearables, such as smartwatches, if the device is designed to interact with the user rather than simply capture data provided by sensors.

Touchscreens offer a new way of navigating through menu items.

A major hurdle for the use of touch-screens as interfaces continues to be the fact that they consume a lot of energy and hence, considerably reduce the portable device's battery life.

“Touchscreens are getting smaller, ultimately provide the same functions as switches, and are definitely set to increasingly expand their market dominance. However, what we won't see is a complete squeeze-out of other options,” predicted Ewing. This is obvious because of the aforementioned energy consumption issue — for every switch removed in favor of the touchscreen option, the device's battery life gets shorter. Also, there is currently no other alternative to electromechanical switches for completely shutting down a device. In other words, the On/Off button is here to stay.

This article was contributed by Panasonic Corporation of America, Newark, NJ. For more information, Click Here .

Tech Briefs Magazine

This article first appeared in the July, 2018 issue of Tech Briefs Magazine.

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